Blood collection and phase separation containers are known in the art, for collecting whole blood and separating the light serum from the heavier cells. Such containers have a compartment for collecting the blood, wherein phase separation occurs during centrifugation, and some kind of maintaining means for maintaining the serum separate from the cells, once centrifuge separation is finished. A valve can also be included to allow the separated serum to flow elsewhere. The maintaining means can be a gel that is formulated or constructed to seek a specific gravity that is in between that of the two phases being separated. Examples of such prior containers are shown in U.S. Pat. No. 4,012,325. Porous mechanical barriers can be used to assist the gel, as shown in U.S. Pat. No. 4,169,060, but these are not effective without the gel, nor are they positioned to work without the gel.
Such containers have been proven to be highly effective. Their only drawback, which has been minor, is the complication created by having to assemble such a device with a gel and/or mechanical barrier that is movable with respect to the compartment. It is desired in such assembly that the gel and/or mechanical barrier be correctly positioned at the start of the operation, to preclude heavier phase material from contacting portions intended to contact only the lighter phase. Thus, more care has been needed in assembly than would be the case if the maintaining means were somehow a fixed feature of the compartment. However, because the ratios of lighter to heavier phase are unpredictable, at least with blood samples, it has been thought impractical to position maintaining means only at one location to satisfy all possible conditions to be encountered. Thus, prior constructions use a movable maintaining means that will seek out its correct position.
Therefore, prior to this invention there has been a need for a phase separation container having fixed maintaining means that will accommodate expected variations in phase volumes, so that the fixed maintaining means can be manufactured automatically while manufacturing the rest of the container.